The big picture: Variation in animal reproduction
- Mating between males and females is boring
- species can reproduce without sex
- individual of species can change sex
- species have male and female sex organs
- some populations have only a few that mate
- Two modes of reproduction in animal kingdom
- Sexual:
- Asexual:
- Animals exhibit cycles of reproductive activity
- Mammalian reproduction is governed by hormones


Asexual reproduction in the animal kingdom
- Budding:
- found among invertebrates
- Fission:
- about the same size
- found among invertebrates
- Fragmentation:
- accompanied by regeneration of lost body parts
- sponges, worms, starfish
- Parthenogenesis:
- found among invertebrates and vertebrates

Review video on budding, fragmentation (+ unnecessary extras)
Parthenogenesis: Male drone bees are fertile and haploid!

Animal sex blurs the lines of male and female
- Sexual reproduction commonly between male and female
- finding a partner is difficult
- Stationary animals tend to be hermaphroditic
- individual have male and female reproductive bits
- Any 2 individuals can mate/self-fertilize
- Sex reversal occurs in different animal phyla
- oysters are males first, then turn to female when larger
- the largest female in some coral fish turn to male

Reproductive cycles are common in the animal kingdom
- Cycles controlled by hormones and environmental cues
- occur with asexual or sexual modes
- usually related to seasons
- Ovulation: release of eggs at midpoint of female cycle
- cycles are variable in length, synced with seasons
- sheep: cycle + pregnancy = birth in spring
- Daphnia: cycles between asexual and sexual
- seasonally related to environment

The “Handicap” of sexual reproduction

How sperm and egg come together…
- Fertilization =
- can be external or internal
- External: eggs shed by the female & fertilized by sperm in the environment
- moist habitat always required
- spawning:

How sperm and egg come together…
- Fertilization:
- can be external or internal
- Pheromones: chemicals used to influence physiology and behavior
- function as mate attractants
- pheromone production in humans is controversial

Pheromones in humans?


Internal vs External: Offspring survival
- Internal fertilization produces fewer gametes
- survival of zygotes higher
- Internal associated with protection mechanisms
- parental care of young
- shells, amniotic eggs, marsupials(?)

Making and delivering gametes
- Individuals usually have gonads that produce gametes
- essential for sexual reproduction
- often established early in embryo development
- Many animals have complex systems
- structures to carry, store, protect and nourish gametes
- e.g. fruit fly (spermathecae stores sperm in female)
- Mating may occur with more than 1 male
- males have mechanisms to prevent other male success

Mammalian reproduction governed by hormones
- Hormones coordinated from many glands/organs
- hypothalamus, pituitary and gonads
- endocrine system
- Gonadotropin-releasing hormone (GnRH) is secreted by the hypothalamus
- directs release of FSH (follicle-stimulating hormone)
- directs release of LH (luteinizing hormone)
- both from pituitary gland
- FSH and LH act on male and female gonads
- stimulate sex hormone production

Mammalian reproduction governed by hormones
- Gonads then produce and secrete 3 hormones
- testosterone, estradiol and progesterone
- found in male/females in different amounts
- Male embryos: direct reproductive structures
- Maturing mammals: induce sex characteristics
- physical/behavior differences (male/female)
- Mature mammals: play role in gamete formation

Hormonal control of male system (negative feedbacks)

Most female mammals have an ovarian cycle
- Some females have linked menstrual cycle
- 10 primates, elephant shrew, some bats, spiny mouse
- Ovarian cycle:
- series of changes in ovaries
- Menstrual cycle:
- endometrium thickens with blood vessels
- preparation for embryo implantation
- if embryo does not implant, endometrium is shed
- Both cycles occur concurrently
- use same series of hormones

